This invention relates to a circuit interrupter and, more particularly, to a circuit interrupter in which the movable contact arm is prevented from bouncing during trip operation.
FIGS. 1 to 4 illustrate one example of a conventional circuit interrupter which has a contact arm stop arrangement similar to the circuit interrupter disclosed in Japanese Utility Model Laid-Open No. 52-11569. FIG. 1 is a sectional side view of the conventional circuit interrupter in the ON position, FIG. 2 is a partly cut-away side view of the circuit interrupter shown in FIG. 1 but in the OFF position, FIG. 3 is a view similar to FIG. 2 but illustrating the TRIP position with the movable contact arm separated, and FIG. 4 is a view similar to FIG. 2 but illustrating the TRIPPING position of the circuit interrupter in which the movable contact arm is being separated.
In these figures, the circuit interrupter comprises an electrically insulating housing 1 composed of a cover 1a and a base 1b on which a stationary contact 2a having secured thereon a stationary contact element 2a is fixedly mounted. A frame 3 is also firmly mounted to the base 1b by screws 4 (only one is shown). The frame 3 supports at its projection 3a an operating handle 5 so that the operating handle 5 is rotatable about the projection 3a. The operating handle 5 has mounted thereon a cradle 6 pivotable relative to the operating handle 5.
A toggle link 8, which includes an upper toggle link 8a and a lower toggle link 8b pivotally connected to the upper toggel link 8a by a knee pin 9, is connected to the operating handle 5 by an upper toggle link pin 7 at the upper end of the upper toggle link 8a. The lower end of the lower toggle link 8b is connected by a pin 12 to a cross bar 11 which is rotatably mounted by the base 1b. The knee pin 9 of the toggle link 8 is biased toward the operating handle 5 by a tension spring 10 connected between the pin 9 and the handle 5, thus maintaining the upper toggle link 8a in engagement with the projection 7. A movable contact arm 13 having a movable contact element 13a secured thereon is rotatably mounted on the cross bar 11 by a shaft 14. The movable contact arm 13 is electrically connected to a terminal conductor 15 through a flexible conductor 16.
The circuit interrupter also comprises an electromagnetic trip device including an electromagnetic device 17 which has a movable plunger 17a. A thermally responsive trip device having a bimetal 18 with an adjusting screw 18a is also provided. In order to pick up the movements of two kinds of trip devices, a trip bar 19 which is rotated by the screw 18a or the plunger 17a is provided. The trip bar 19 is in engagement with a latch 20 which is in engagement with a latch 21 which releasably latches the cradle 6.
The conventional circuit interrupter further comprises a toggle link stopper 23 pivotally mounted on the frame 3 by a pivot pin 28. The toggle link stopper 23 has a stop surface 23a at which the side edge of the upper toggle link 8a abuts during tripping of the circuit interrupter. The toggle link stopper 23 also has a surface 23b at which the stopper pin 22 secured on the frame 1 abuts in order to prevent the toggle link stopper 23 from being moved beyond a predetermined position.
When the circuit interrupter is in the ON position shown in FIG. 1, the current flows from the stationary contact 2 to the terminal conductor 15 through a stationary contact element 2a, the movable contact element 13a, the movable contact arm 13 and the flexible conductor 16. When the operating handle 5 is moved in the direction of an arrow 24, the upper end of the tension spring 10 is moved beyond dead center of the line of action of the spring 10, causing the tension spring 10 to collapse the toggle link 8 to move the movable contact arm 13 upwards together with the cross bar 11 until the operating mechanism takes the position shown in FIG. 2.
When a very large current flows through the circuit interrupter in the ON position shown in FIG. 1, the electromagnetic trip device is actuated to push out the plunger 17a from the electromagnetic device 17. Alternatively, when an overcurrent flows through the circuit interrupter in the ON position shown in FIG. 1, the thermally responsive trip device is actuated to push the trip bar 19 by the adjusting screw 18a. In either case, the trip bar 19 is rotated to rotate the latch member 20 and then the latch 21 rotates to release the cradle 6 under the action of the spring 10 which biases the cradle 6 to rotate clockwise. The cradle 6 is then rotated in the direction of an arrow 25 shown in FIG. 3 so that the toggle link pin 7 moves overcenter causing the toggle link 8 to collapse to rotate the movable contact arm 13 together with the cross bar 11 about the shaft 14 until they are brought into the TRIP position shown in FIG. 3 in which the movable contact element 13a is separated from the stationary contact element 2a.
When the movable contact arm 13 reaches the position beyond which further contact opening movement is prevented, the movable contact arm 13 bounces back toward its original position as shown by an arrow 26 in FIG. 3. However, the link stopper 23 which abuts at its stop surface 23a against the side edge of the upper toggle link 8a as shown in FIG. 4, prevents the further straightening of the toggle link 8 beyond the position shown in FIG. 4 thereby limiting the return movement of movable contact arm 13.
With the conventional stopper arrangement as above described, the stop surface 23a of the link stopper 23 engages the upper toggle link 8a only when the movable contact arm 13 is returning from the bouncing as shown in FIG. 4, and the stop surface does not engage the toggle link 8 during the contact trip-opening movement of the movable contact arm 13, providing only a relatively small stopping ability. Therefore, when the movable contact arm 13 is bounced with a greater force, the upper toggle link 8a of the toggle link 8 often cannot be stopped by the link stopper 23, allowing the movable contact element 13a to be brought back into contact with the stationary contact element 2a, resulting in a failure in current interruption.